1. Field of the Invention
Two-cycle engine accessories
2. Description of the Prior Art
Occasionally a descriptive term in this application may be shortened so as to recite only a part rather than the entirety thereof as a matter of convenience or to avoid needless redundancy. In instances in which that is done, applicant intends that the same meaning be afforded each manner of expression. Thus, the term gas pressurizing control cylinder (4) might be used in one instance but in another, if meaning is otherwise clear from context, expression might be shortened to control cylinder (4) or merely cylinder (4). Any of those forms is intended to convey the same meaning. The term attach or fasten or any of their forms when so used means that the juncture is of a more or less permanent nature, such as might be accomplished by bolts, welds or adhesives. Thus it is stated herein that the pneumatic exhaust control piston (40), where interthreading is employed as the means of connection, is attached to the combustion cylinder (200). A connection in which one object is easily removed from another is described by the word emplace, as where it is stated herein that the sliding tongue (2) is partially emplaced within the exhaust port (203) during a particular phase of operation. Employment of the words connect or join or any of their forms is intended to include the meaning of both in a more general way.
The term rigid emplacement denotes a connection other than by attachment which, nevertheless, permits separation only with considerable difficulty. It is accordingly stated herein that the connection of the spring (3) to the spring seating bolt head (32) at the spring abutment zone (31) is one of rigid emplacement
The word comprise may be construed in either of two ways herein. A generic term used to describe a given one of a number of specific elements is said to comprise it, thereby characterizing the specific element with equivalency in meaning for the generic term. Thus, means (300) to emplace the sliding tongue (2) within the exhaust port (203) may be said to comprise the spring (3), meaning that in the particular case, the means (300) is that particular object (3) as opposed to some other, such as an operably manipulated cable or a servo-mechanism of some sort. However, the word comprise may also be used to describe a feature which is part of the structure or composition of a given element. Thus, a shock absorbing gas pressurizing control cylinder (4) may be said to comprise a pneumatic chamber (44), meaning that the structure of the cylinder (4) is such as to have the pneumatic chamber (44) as a feature of its structure. The meaning in the respective cases is clear from context, however. Accordingly, modifying words to clarify which of the two uses is the intended one seem unnecessary.
Terms relating to physical orientation such as , up, down, higher and lower refer to the positioning of an engine part in the manner in which it is typically mounted in a vehicle and consistent with the manner the subjects of this application are shown in the drawings. Thus, the exhaust port (203) is frequently spoken of as being disposed proximate the top of the combustion cylinder (200) and the intake port as being disposed at the bottom thereof (200). Consistent with this is the reference, supra, to "raising" the exhaust port (203) as a design remedy.
The term effectually open and effectually closed, is used herein with reference to the degree of obstruction of the sliding tongue (2). The tongue (2) is stated herein to effectually open and effectually close the exhaust port (203). The use of such terminology acknowledges the fact that even when the tongue (2) is brought to its maximum interference point within the port (203), a substantial opening necessary to allow the flow of sufficient exhaust for engine idling remains. Although the tongue's (2) closure may not, therefore, be complete, it may correctly be said to be effectually so. Conversely, although the tongue (2) may have not been withdrawn completely from the port (203) during high RPM operation, maximum airflow may have, nevertheless, have been attained. At that height, the tongue (2) is stated herein to be effectually open.
The two-cycle engine known to prior art has widespread application including several varieties of lawn mowers, snow throwers, snowmobiles, water craft and other sports vehicles. Such an engine enjoys economy in production in that several valves and other moving parts are eliminated therefrom. The body of the piston (201) itself conveniently blocks and unblocks ductwork communicating with the combustion cylinder (200) as it (201) reciprocates in advance and withdrawal within the cylinder (200). It is universally recognized that at high powered operation involving numerous revolutions per minute (RPM), maximum power may be attained--or at least approached--if the end products of combustion, or exhaust, are expeditiously removed from the engine. An engine built to accommodate that result, however, encounters difficulty at low RPM, where the enlargement of the exhaust port (203) diminishes air velocity much in the same manner experienced with the slower ejection rate of water from a substituted garden hose of greater diameter than that otherwise employed. Differences in air velocity are associated with what is commonly regarded as "throttle response" or "quickness" At low RPM, advantage is gained by reserving at least a portion of the exhaust to interfere with the combustion process. Accordingly, compromises have had to be made in manufacture to attain acceptable performance at what might be considered either end of the spectrum.
An engine dedicated to acceptably smooth performance at low RPM, therefore, necessarily loses something at high RPM. Where high RPM performance is a priority, efforts undertaken to recover what is otherwise foregone entail, for example, "raising the ports"--that is, enlarging the top parameter of the exhaust port (203) so that it (203) becomes and remains at least partially unblocked by the combustion piston (201) during a longer portion of the combustion cycle. Thus, in terms of a 360 degree combustion piston (201) stroke, approximately as much as 25 degrees may be added. The matter is also frequently addressed in terms relating to the "timing" of the cycle or "pulse activation" and, not surprisingly, efforts have been undertaken to address the low RPM end of the spectrum by spoiling, as it were, the precise timing of the engine otherwise demonstrated at high RPM.
Novel devices have been introduced over recent decades to interfere mechanically with the otherwise efficient discharge of exhaust at low RPM and to enhance it mechanically at high RPM. The most promising appears to comprise a device attached to the combustion cylinder (200) which regulates power by moving a mechanical obstructor into--or conversely out of--the exhaust path. Because of its configuration and manner of operation, such a device has occasionally been referred to as a "guillotine".
The airflow comprises a cycle in which the fuel, air and oil mixture passes through the combustion cylinder's intake port (207), becomes pressurizing gas (202) as a result of the combustion piston's (201) operation and ultimately emerging as spent gas through the exhaust port (203). When the obstructing device is emplaced for maximum blockage of the exhaust port (203), the increase in air velocity enhances carburetor efficiency.
The transition between maximum blockage at low RPM and an effectually open position at high in many of the prior art devices is too abrupt for the carburetor to keep up with, however. A properly configured system should be capable of producing smoother transition between the two extremes to maximize carburetor performance.
Early developments produced a manually controlled cable which operably manipulated the obstructing device for the effect desired. It was eventually discovered that electro-servo mechanisms--or alternatively, even a simple spring--could be installed to impel the obstructing device partially into the exhaust port (203). The converse action, partial or total withdrawal of the device therefrom (203) could be accomplished by utilizing the compression force of the precombustion gas to effectually blow the obstructor out of the way. In some cases, accordion-like "boots" or bellows were employed; in others, merely a pivotable flap. Some inventors focussed upon rotating obstructors positioned to move where required during the power cycle. Some devices actually relied upon displacement of an obstructing mechanism by trip action effected by the combustion piston's contact with it--that is, by effectually knocking it into or out of blocking position. Some of the devices responded in lock-step with the rhythm of combustion, such that with each cycle, they underwent a corresponding reciprocating movement.
It must be recognized, of course, that the combustible mixture present within the system comprises a suitable mixture of gasoline and oil dispersed throughout ambient air and that the exhaust produced therefrom comprises spent combustion end products. In operation, some residual exhaust undoubtedly mixes with the combustible mixture present. The mix of gas undergoing compression as the combustion piston (201) advances is referred to herein as pressurizing gas (202).
It should be recognized that the preferred automatically variable compression devices designed for exhaust port power control do not function at a rate associated with engine revolutions. Thus, at high RPM, the mechanical parts of the device do not themselves reciprocate in rhythm as in the case of some devices referred to supra. Rather, it is because the combustible compression produced at high RPM is substantially greater than that produced at low RPM that such preferred devices are impelled to one position or another. The compression associated with high RPM, thus, preferably causes such an obstructor to move to a position which allows essentially unrestricted exhaust emission. At low RPM, compression drops and some device--a spring in some cases, a servo mechanism in others--should cause the obstructor to move to a position which restricts the mass of exhaust, thereby increasing its velocity so as to enhance low speed operation. During a sustained episode of high RPM, the obstructor remains in a generally fixed position by which the exhaust port (203) is widely opened. At sustained low RPM, the obstructor again remains in a generally fixed position, but partially restricting the exhaust port (203). At intermediate RPM, a corresponding intermediate result is achieved.
Some of the prior art devices relied heavily upon hydraulic control mechanisms. Often, many of them have been prone to popping open and slamming shut, lacking the smoothness desired in operation.
U.S Pat. No. 5,904,122 issued to Hoyd entailed an attractive and in other respects efficient exhaust emission control valve relying upon an operator's manual adjustment to effect a desired setting for the device. So far as operably manipulated devices are concerned, that one demonstrated considerable improvement over those involving throttle knobs and cords or like devices which diverted the operator's attention from controlling the vehicle's movement in a more general way. An even greater improvement, of course, would be an assembly which obviates even such pre-operation setting manipulation.
Some of the historical efforts at exhaust control involved drastic engine reconfiguration, offering even the remarkable remedy of shifting engine lobes or chambers--referred to as "epochoidal" surfaces--so as to increase or decrease combustion cylinder (200) volume. For the degree of complexity involved, U.S. Pat. No. 4,202,297 issued to Oku, et al, appeared reasonably early, comprising special configuration within or immediately about the combustion chamber (200). The Oku, et al device is a two-piece one requiring considerable attention in assembly.
U.S. Pat. No. 3,799,498 issued to Wickham; U.S. Pat. No. 5,337,707 issued to Blundell, et at, and U.S. Pat. No. 5,678,404 issued to McManus all feature servo-mechanisms to control partial exhaust port (203) blockage. The Wickham device employs an elastic diaphragm reactive not to pressures which are pneumatic but rather, hydraulic.
U.S. Pat. No. 4,321,893 issued to Yamamoto refers to prior art incorporating exhaust port (203) control through an operative throttle and itself comprises a mechanical governor apparatus dedicated to that end.
U.S. Pat. No. 4,033,378 issued to Pauliukonis; U.S. Pat. No. 4,776,305 issued to Oike; and U.S. Pat. No. 4,970,997 issued to Inoue, et. al all employ one form or another of mechanical spring action for either direct or indirect exhaust port (203) control, the Oike spring applying resilient bias not upon an exhaust port (203) obstructor but against a cam with which it cooperates. The Pauliukonis device also depends upon cam action. The Inoue, et al patent features some degree of control over the resiliency of the spring itself.
Devices which are at least partially controlled pneumatically are shown in U.S. Pat. No. 4,285,357 issued to Jones and U.S. Pat. No. 5,218,819 issued to Cruickshank. The first of the two illustrates a device comprising an elastic diaphragm as the exhaust port (203) obstructor itself. The second, one also employing a diaphragm comprising "baffle" construction operating in cooperation with a rotating shaft mechanism for exhaust control.
Other pneumatically controlled devices of interest include U.S. Pat. No. 4,364,346 issued to Shiohara, U.S. Pat. No. 5,588,402 issued to Lawrence and U.S. Pat. No. 5,873,344 issued to Heinrich. All three include an exhaust port obstructing plate which is caused to protrude angularly into and retract from the port to a varying extent, thereby reducing or increasing, respectively, the volume of exhaust emitted from the system. The Shiohara patent, unfortunately, fails to describe the control mechanism which moves the plate, asserting the assumption that prior art has already provided what is necessary.
Both of the other patents rely upon an elastic diaphragm responsive to combustion fuel-air pressure. The Lawrence device, claiming optionally to feature an electronic sensor, employs as the source of pressure used to energize the diaphragm that within the engine's intake section. The Heinrich valve uses pressure within the combustion chamber itself.
Although pneumatic control systems deriving their energizing force from the exhaust port itself are known in the art, the immediately foregoing inventors of such devices hoped to avoid what they considered objectional shortcomings by enslaving gas pressure from the alternative sites chosen by them. One of the objections, for example, has been the proposition that exhaust gas contains unwanted oil droplets or other contaminating combustion byproducts. A sufficiently innovative design, however, might well meet that challenge.
In a sense, it may well be that the intended shift from an exhaust port gas source to some other in the engine may be recognized in the old adage of throwing the baby out with the bath water. The mechanisms devised to accomplish the task entail difficulties which may fairly be said to at least equal those of their predecessors. By their nature, diaphragms comprise a flexible composition prone to wear with continued use and, quite often, chemical decomposition with age. Complex ducting is required to transport the pressurized gas to its intended diaphragm site. Unfortunately, the ductwork is made to comprise a comparatively long tunnel disposed within the engine block. Judging by the prior art, it is apparently impractical to route the pressurized gas through external tubing. Then, a second tunnel is also generally included in order to provide dampening desired--if not required absolutely--for smooth operation.
What is needed is a pneumatically energized valve relying upon exhaust port gas as its source but which does not require the manufacturing expense of drilling or casting a conduit into the engine block; and a dampening mechanism which does not rely upon a second such conduit but instead employs waste exhaust oil droplets in accomplishing its function.
A review of the foregoing sequence of development demonstrates clearly the vigor with which the exhaust control problem has been addressed. Nevertheless, the needs or objectives pointed out supra thus far remain only partly addressed in the prior art. Some, such as that just immediately discussed, have not been met at all.